Take #2 on Electromagnetic Doohicky

Thread Starter


Joined May 16, 2005
I'm further along in designing the "toy" from the "I-Bridge" thread. Doing the math for this made me realise some changes were in order...

To make sense of things, I offer the following explanation:

ARM1, ARM2, and ARM3 are not actually individual components, but are adjacent places on a long, movable coil. (This will be a laquered piece of 5/8-18 threaded rod wound with bare 16gage wire.) Resistance is negligable, about 27 milliohms for ARM2.

STAT1 is a one pound spool of AWG24, resistance is about 20 ohms.

Commutators 1 and 2 are on one side of the spool, Commutators 3 and 4 on the other.

The threaded rod will go through the middle of the spool.

I want the threaded rod to move up or down, based on the signals applied to the totem-poles. (Unless I've got the thing horizontal - then it would be "to and fro.")

R1 and R2 limit base current of Q1 through Q4 to 4.4mA

D1 through D4 are snubbers.

D5 and D6 keep the mosfet gates from going above 5.1v. I'll probably dispense with these. (IRF840 can withstand 30v gate to source!)

I-bridge 2.jpg


Joined Apr 20, 2004

Looks kike it will switch properly. Don't know what you have to move, but using a nice rare-earth magnet inside a coil makes for nice movement. If you can find a cylindrical one, it might be easy to incorporate an operating rod. The tighter the clearances, the better the fields react.

Of course, doing it the hard way can be part of the fun, too.